P1650: METABOLIC ABNORMALITY AND GLUCOCORTICOID RECEPTOR MODULATION OF MYELOID-DERIVED SUPPRESSOR CELLS IN IMMUNE THROMBOCYTOPENIA PATIENTS AND AN ACTIVE MURINE MODEL
Authors: S. Wang, J. Peng
Journal: HemaSphere (2022)

Background: Immune thrombocytopenia (ITP) is an autoimmune hemorrhagic disorder in which pathologic antiplatelet antibodies bind to platelets and mark them for phagocytic breakdown, and imbalanced T cell subsets are also involved in its pathogenesis. Myeloid-derived suppressor cells (MDSCs) are circulating immature myeloid cells that suppress T-cell responses and play an important role in the immunopathogenesis of ITP. Glucocorticoids have been widely used for ITP treatment, however, approximately 30% of patients fail to respond to the glucocorticoid treatment or relapse in a short period. The biological action of glucocorticoids is mediated by glucocorticoid receptor (GR); however, the underlying mechanism of glucocorticoid-resistance remains unknown. Aims: To investigate the role of GR in abnormal metabolism of MDSCs in glucocorticoid-resistant ITP patients. Methods: We enrolled 36 ITP patients with newly diagnosed ITP who had received glucocorticoid treatment. For immunostaining of MDSCs’ mitochondria, human MDSCs were generated in vitro, stained with MitoTracker Red and anti-CD33 antibody. In addition, quantitative real-time RT-PCR and immunoblotting analysis were performed to analyze the expression of GR and CPT-1 at the mRNA and protein levels, respectively. And we prepared GR-silence MDSCs to explore the function of GR in MDSCs metabolism and transferred them into an active ITP murine model. Flow cytometry analysis was performed to detect T cell subsets of active ITP mice. Results: The mean fluorescence intensity of MitoTracker Red was significantly weaker in CD33+ cells from patients with glucocorticoid-resistant ITP, indicating lower levels of mitochondrial physiology than healthy controls and glucocorticoid-sensitive patients. The expression of GR and CPT-1 were also decreased at both the mRNA and protein levels in those with poor response to glucocorticoids. Moreover, we performed an siRNA transfection test, targeting GR in WT murine MDSCs. Results showed that the expression level of CPT-1 was significantly lower in GR-siRNA treated MDSCs (GR-MDSCs) than that in NC-siRNA treated MDSCs (NC-MDSCs), indicating that the decreased expression of CPT-1 was affected by down-regulated GR in MDSCs. The active ITP murine model exhibited profound thrombocytopenia, and their platelet count decreased significantly by the second week after irradiation. Mice received GR-MDSCs treatment displayed significantly lower platelet levels than mice treated with NC-MDSCs. Subsequently, spleens were harvested from ITP mice at day 28 after irradiation, flow cytometry analysis revealed that the percentage of CD8+ T cells in mononuclear cells and Th1 cells in CD4+ T cells decreased significantly in the spleen of mice who received NC-MDSCs than GR-MDSCs, while the percentage of Tregs and Th2 in CD4+ T cells were increased in NC-MDSCs treated mice. Summary/Conclusion: This study shed new light on the molecular mechanism of glucocorticoid-resistant of ITP patients that GR regulated mitochondrial metabolism of MDSCs, which modulated the immunosuppressive functions of MDSCs. This could possibly provide novel therapeutic targets for patients with poor response to glucocorticoids.